MB-7522 Further test improvements/coverage

Verify that the state transitions don't restart the updater
during incremental index updates as well (instead of only
initial index updates).

Change-Id: Iea677e75217d7e4f927cd4c503dd4487cff790ba
Reviewed-on: http://review.couchbase.org/23899
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>